Generally, in a nailing machine constituting a power source by compressed air, a strike piston integrally connected with a driver for striking a nail is arranged by being contained slidably at inside of a strike cylinder, by supplying compressed air stored at inside of an air chamber connected to a compressed air supply source to inside of the strike cylinder, the strike piston is impulsively driven at inside of the strike cylinder, and a nail is struck by a driver connected to the strike piston. In addition, in order to supply compressed air for driving the strike piston to inside of the strike cylinder and exhaust compressed air after driving the strike piston from inside of the strike cylinder, an upper end portion of the strike cylinder is provided with a main valve for selectively connecting inside of the strike cylinder to the air chamber and an exhaust port connected to the atmosphere.
Normally, such a main valve is constituted as a head valve arranged on an upper side of the strike cylinder, a lower end face of the head valve is brought into close contact with an upper end face of the strike cylinder to thereby close an interval between inside of the strike cylinder and the air chamber. Compressed air is supplied to inside of the strike cylinder by communicating the interval between the air chamber and the strike cylinder by separating the lower end face of the head valve from the upper end face of the strike cylinder by operating the head valve to an upper side. Therefore, the head valve is arranged at a position on an upper side of an upper end of the strike cylinder as a whole, and a dimension capable of moving the head valve to the upper side is needed.
When the head valve is arranged at the position upward from the upper end of the strike cylinder as described above, a total height of the nailing machine needs to be formed to be large by an amount of a dimension of the head valve and a dimension of operating the head valve to the upper side. For example, when one wall frame is connected to other wall frame by a nail in 2×4 construction method or the like, as in a case of connecting the one wall frame to a floor by a nail, there is a case in which the nailing machine cannot be used at a narrow place restricting the total height of the nailing machine as in connecting one wall frame to a floor by a nail.
JP-Y-06-045336 discloses a nailing machine in which a total height of the nailing machine is reduced by reducing a dimension upward from a strike cylinder by arranging a main valve mechanism at a surrounding of an upper end portion of the strike cylinder in order to prevent the total height of the nailing machine from being increased as described above. According to the nailing machine, there is constructed a constitution in which the main valve is formed in a ring shape to be able to slide along an outer peripheral face of the strike cylinder, an outer peripheral face remote from an upper end of the strike cylinder to a lower side is formed with a valve seat for supplying air and a valve seat for exhausting air to be opposed to the valve seat for supplying air at a predetermined interval therebetween, a valve member portion for supplying and exhausting air in a ring shape formed at the main valve is arranged between the valve seat for supplying air and the valve seat for exhausting air, and the valve member portion for supplying and exhausting air of the main valve is made to seal selectively the valve seat for supplying air and the valve seat for exhausting air by a face thereof.
According to the nailing machine of JP-Y-06-045336, a ring-shaped member in a sleeve-like shape is arranged at an outer periphery of the strike cylinder by maintaining a predetermined interval from a side of the outer peripheral face of the strike cylinder to thereby form an intake/exhaust path for guiding compressed air to inside of the strike cylinder by an inner peripheral face of the ring-shaped member and the outer peripheral face of the strike cylinder. Moreover, a lower end face of the ring-shaped member is mounted with a seal member made of rubber for forming the valve seat for exhausting air engaged with the valve member portion for supplying and exhausting air of the main valve.
Meanwhile, there is a nailing machine of a recent time using compressed air in a high pressure region higher than a normal pressure lower than 10 kg/cm2 in the pressure of the compressed air as a power source. According to the nailing machine used by compressed air at such a high pressure, there is a case in which high pressure compressed air supplied from a compressed air supply source at high pressure to inside of an air chamber of a nailing machine is expanded at inside of the air chamber, water included in compressed air is frozen by a temperature drop by the adiabatic expansion and small ice particles are produced at inside of compressed air in the air chamber. The ice particles included in compressed air are adhered to the inner peripheral face of the ring-shaped member and the outer peripheral face of the strike cylinder when compressed air flows to inside of the strike cylinder by opening the head valve, the ice particles gradually grow to be large and deposited on seal faces of the valve seat for sucking air and the valve seat for exhausting air and the head valve is failed to be operated by a failure in seal or leakage of air.